John Matthews is a gifted wordsmith, and he has written many books. However, what he writes is not handed down from any Celtic tradition. He has taken Michael Harner's core shamanism and, in place of North American Indian images, Matthews has substituted a variety of unrelated motifs and images from Welsh, Irish, and Arthurian tales. For example, Matthews substitutes the "crane bag" of Mannanan Mac Lir (an Irish figure) for the medicine bag that Harner adopted from various indigenous peoples. There is no evidence that Irish religious figures ever had "crane bags," and the symbol is not found in any other Celtic tradition. Yet on Matthews goes, mixing images and symbols from various eras and traditions, ignoring their integrity and twisting them to suit his purposes. Almost any meditative technique will produce certain results, and you may find that Matthews' techniques (in this book and others) work for you. However, what you will be using is an adaptation of Harner's core shamanism, not anything passed down from Celts of any tradition. You might as well read Harner's book _The Way of the Shaman_ or take a course from him and substitute whatever symbols appeal to you. For accurate examination of shamanic elements and behaviors in various Celtic traditions, see L.E. Jones' _Druid, Shaman, Priest_.
John Matthews is an important New Age writer on Celtic and Arthurian topics, and has written some valuable books on Celtic 'Shamanism'. Unfortunately, this book is essentially a reworking of Michael Harner's 'core shamnism', dressed up in some Celtic motifs. While that approach may be useful for beginning students, it shouldn't be mistaken for actual Celtic practice.